The present invention relates generally to cable ties and relates more particularly to cables ties formed from two separately molded plastic components.
Cable ties, also known as bundling ties and harnessing devices, are well known devices commonly used in the art to couple together a plurality of elongated objects, such as wires or cables. One type of cable tie which is well known and widely used in the art comprises an elongated strap having an apertured head disposed at one end thereof. The opposite end of the elongated strap is typically shaped to define a tail of narrowed width adapted for insertion through the apertured head to form a closed loop. A plurality of serrations or teeth are formed along the length of the elongated strap, and an internal pawl (or locking tang) is disposed within the apertured head, the internal pawl being adapted to sequentially engage the serrations on the strap. In this manner, the engagement of the internal pawl with the serrated strap is used to lock the cable tie in a closed loop configuration.
Cable ties are typically formed by injection molding. More specifically, this typically involves the use of a two-piece mold into which the impression of one or more whole cable ties has been formed. Molten plastic, such as nylon, polypropylene or the like, is injected into the mold through a single opening or gate in the mold until the one or more impressions therein are filled. The molten plastic is then allowed to harden in the one or more impressions. The thus-formed cable ties are then removed from the mold.
Use of the aforementioned injection molding technique to construct cable ties suffers from a couple of notable drawbacks.
As a primary drawback, the above-described process involves molding the entirety of a cable tie through a single injection molding step. As a result, the length of the cable tie strap is limited by the size of its corresponding impression. Consequently, to make a variety of cable ties having straps of different lengths, it is generally necessary to use a plurality of different sized impressions. This typically results in the need for many differently-sized molds to be constructed. As can readily be appreciated, the provision of many differently-sized molds may be prohibited by cost as molds are very expensive to produce.
As a secondary drawback, because the above-described process requires that the entirety of the cable tie be formed at one time, cable ties having long strap lengths (i.e., several feet) require correspondingly large molds. Molds of such large size are particularly expensive to produce. In addition, because cable tie molds typically have only a single gate through which molten plastic is injected, the cycle time can be rather long as the molten plastic must travel through the single gate in the mold until it fills the entireties of all of the impressions. In addition, the aforementioned forcing of the molten plastic through the entireties of the impressions often results in some degradation of the molten plastic material, such degradation being undesirable.
Accordingly, it is known in the art for cables ties to be formed from two separately molded plastic components, this type of cable tie being commonly referred to in the art as a two-piece cable tie. Specifically, the head portion and the strap portion of each tie are independently formed through separate molding processes. In a subsequent or simultaneous step, the separately formed head and strap are permanently joined together to create a unitary finished product. Accordingly, various custom-length cable ties can be readily constructed without the use of uniquely-designed molds by (i) forming a plurality of straps, each strap preferably being of a considerable length, (ii) cutting each strap to a desired length and (iii) joining each re-dimensioned strap to a universal head. In this manner, it is to be understood that a plurality of different sized cable ties can be created using a single mold for each of the head portion and the strap portion, which is highly desirable.
There presently exists numerous methods in the art for joining together the separately formed head and strap portions of a two-piece cable tie.
As a first connection method, it is well known in the art for the head and strap portions of a two-piece cable tie to be permanently joined together by positioning one end of the strap on or within a portion of the head and, in turn, driving a metal rivet through the overlying segments. Even though a metal rivet adequately retains the head and strap portions of a two-piece cable tie together, it has been found that the cost associated with both the metal material requirement and the complex mechanical driving process renders the rivet connection method unfavorable for mass production.
As a second connection method, it is well known in the art for the head and strap portions of a two-piece cable tie to be permanently joined together using insert molding. For example, in U.S. Pat. No. 6,863,855 to T. Shilale (hereinafter the '855 patent), the disclosure of which is incorporated by reference, there is disclosed a method of constructing a two-piece cable tie which comprises the steps of (i) forming a length of strap material using a rotary extrusion process, (ii) cutting the length of strap material into individual straps of desired length, and (iii) insert molding a front portion, which includes the head, around one end of each individual strap.
The present inventors have found that two-piece cable ties of the type described in the '855 patent suffer from certain performance limitations. Specifically, the present inventors have found that two-piece cable ties of the type described in the '855 patent have a limited load rating. As defined herein, the “load rating” of a cable tie relates to the amount of force that the tie is able to exert/withstand as a closed loop around a bundle without experiencing failure. It has been found that cable tie failure typically occurs as a result of either (i) severance of the strap at some point along its length (referred to hereinafter simply as “strap failure”), (ii) disengagement of the pawl from the serrated strap (referred to hereinafter as “pawl failure”), and/or (iii) separation of the portion of the head that is insert-molded around the strap (referred to hereinafter as “insert-mold failure”).